The best way to keep your MYM safe is by making frequent backups. MYM has an "assistance backing up" screen when exiting MYM, but this utility won't run in an emulator. I created a backup utility called MYMBack.exe which will automatically run when exiting MYM and create a folder stamped with the date and time to be sure you never overwrite your old dataset backup. You can maintain these backup folders as you'd like from Windows Explorer.
You can download the utility here. You may need to update the settings for this file for security reasons because it is unsafe to download exe files from the internet and Windows will attempt to protect you. If you cannot download the MYMBack.exe file directly, you can download the MYMBack.zip file here and extract the MYMBack.exe file from the contents of the zip file.
The first time you run MYMBack.exe, it will ask you for information about where MYM is installed, the Dataset name you want to back up and the location you want to put the backup folder. These initial settings will be saved for the next time you run the utility to speed up the backup process.
I added a call to MYMBack to my MYMLOCK.BAT file which runs every time I exit MYM to prompt me for backing up my data. Here's what my MYMLOCK.BAT file looks like:
@echo off
rem ************Will prevent starting MYM more than once while running
rem *************in Windows.
rem ************Place copy of this batch file in MYM directory.
rem *********** Select MYM icon.
rem *********** Select PROPERTIES in Program Manager FILE menu.
rem *********** On command line enter MYMLOCK.BAT
rem *** Change the following lines to match your MYM path ***
c:
cd\mym12
rem *********** Check to see if inuse.flg exists
if exist inuse.flg goto running
rem *********** Creates file called inuse.flg
echo anything>inuse.flg
LOADHIGH mym.exe
rem *********** Deletes inuse.flg file at normal end of job.
echo Reset inuse.flg to indicate MYM is done running.
del inuse.flg
echo Starting backup...
pause
MYMback
goto end
:running
echo MYM is already running!
pause
:end
@echo on
exit
And, if you use DropBox, a great place to send your backup folder from MYMBack.exe is to your DropBox folder so it gets backed up and stored for you automatically.